Refrigerant circuit

ABSTRACT

Disclosed is a refrigerant circuit which comprises a compressor ( 15 ), a water heat exchanger ( 16 ), a receiver ( 18 ), an expansion valve ( 19 ), and an evaporator ( 20 ). In the refrigerant circuit, a refrigerating cycle is carried out by compressing refrigerant to above a critical pressure in the compressor ( 15 ). A cooling section ( 17 ) for cooling refrigerant flowing out of the water heat exchanger ( 16 ) is provided on the upstream side of the receiver ( 18 ). A part of the evaporator ( 20 ) functions as an air heat exchanger which operates as the cooling section ( 17 ). The cooling section ( 17 ) exchanges heat with refrigerant on the outlet side of the evaporator ( 20 ).

TECHNICAL FIELD

[0001] This invention is directed to refrigerant circuits for use inheat source units of, for example, hot water supply apparatus of theheat pump type.

BACKGROUND ART

[0002] Referring first to FIG. 27, there is illustrated a commonly-usedhot water supply apparatus of the heat pump type. This conventional hotwater supply apparatus is made up of a tank unit 71 having a hot waterstorage tank 70, and a heat source unit 73 having a refrigerant circuit72. The refrigerant circuit 72 is provided with a compressor 74, acondenser 75 which is a water heat exchanger, a receiver 76, anexpansion valve 77, and an evaporator 78. On the other hand, the tankunit 71 is provided with the hot water storage tank 70 and a circulationpath 79. A pump 80 and a heat exchange path 81 are inserted in thecirculation path 79. In this case, the heat exchange path 81 is formedby the water heat exchanger 75.

[0003] Accordingly, when the compressor 74 is activated while the pump80 is activated (operated), stored water (warm water) starts flowinginto the circulation path 79 from a water intake port provided at thebottom of the hot water storage tank 70 and circulates through the heatexchanging path 81. At this time, the warm water is heated (boiled) bythe condenser (water heat exchanger) 75 and is directed back to theupper part of the hot water storage tank 70 from a hot water supplyport. Hereby, high temperature warm water is stored in the hot waterstorage tank 70.

[0004] Hitherto, as the refrigerant of a refrigerant circuit of the typedescribe above, various refrigerants, such as dichloro difluoro methane(R-12), chloro difluoro methane (R22) et cetera, have been used.However, alternative refrigerants, such as 1,1,1,2-tetra fluoro ethane(R-134a) et cetera, are now being used to cope with problems, e.g.,ozone layer destruction and environmental pollution. However, therefrigerant R-134a is still problematic because it exhibits a highglobal warming potential. Accordingly, use of natural refrigerants freefrom these environmental problems has been recommended. The fact thatsuper-critical refrigerants such as carbon dioxide gas are useful asnatural refrigerant has been known in the art. By the term“super-critical refrigerant” used here is meant a refrigerant whichperforms a refrigerating cycle by compression to above a criticalpressure in the compressor.

[0005] Problems to be Solved

[0006] Referring to FIG. 26, there is graphically shown therefrigerating cycle of a refrigerant circuit employing a super-criticalrefrigerant such as carbon dioxide gas. And now, when hot water (warmwater) is being boiled, high temperature hot water (warm water) flowsout into the circulation path if high temperature warm water is storedto the bottom of the hot water storage tank, with the result that thetemperature of water entering into the water heat exchanger 75 rises.Such a rise in the temperature of water entering into the water heatexchanger 75 results in a refrigerating cycle shown by a solid line ofFIG. 28. Consequently, the enthalpy difference becomes narrowed in acondensation process (heat liberation process), therefore resulting inthe reduction in hot water supply capacity and COP (coefficient ofperformance).

[0007] In addition, as shown in FIG. 29, the rise in outside airtemperature also causes the refrigerating cycle to become narrowed inoperational range.

[0008] In other words, various circumstances cause variations in load onthe condensation side (heat liberation side) and on the evaporationside. Such load variation causes a stable refrigerating cycle to undergoa change. Consequently, each refrigerating cycle requires a differentamount of refrigerant from the other. Even if the refrigerant is chargedfor a certain refrigerating cycle, the refrigerating cycle will changedepending on the operational status. As a result, the amount of chargedrefrigerant may be in excess or deficiency, and there is the possibilitythat the refrigerating cycle is not maintained adequately.

[0009] As described above, in a refrigerating cycle in which therefrigerant is compressed to above a critical pressure and high pressurebecomes a so-called super-critical cycle, the refrigerant densityvariation in a super-critical zone becomes continuous. Therefore,conventional techniques find it difficult to deal with an excessrefrigerant generated in an operational area of a different operationalcondition. If such an excess refrigerant is not dealt with, there is thepossibility that wet operation is carried out. The wet operation causesthe drop in discharge temperature of the compressor 74, with the resultthat the refrigeration effect is reduced and the COP falls. In order tosolve these problems, the design pressure must be made higher, which isexpensive.

[0010] The present invention was made to eliminate the above-describeddrawbacks. Accordingly, an object of the present invention is to providea refrigerant circuit capable of maintaining the refrigerating cycleadequately in various operational situations.

DISCLOSURE OF INVENTION

[0011] Accordingly, a first invention provides a refrigerant circuitcomprising a compressor 15, a radiator 16, a receiver 18, an expansionvalve 19, and an evaporator 20, and in the refrigerant circuit thecompressor (15) compresses refrigerant to above a critical pressure forperforming a refrigerating cycle. And, a cooling section 17, for coolinga refrigerant flowing out of the radiator 16, is disposed on theupstream side of the receiver 18.

[0012] Stated another way, the first invention is directed to arefrigerant circuit which is made up of the foregoing components, i.e.,the compressor 15, the radiator 16, the receiver 18, the expansion valve19, and the evaporator 20. The refrigerant circuit of the firstinvention uses, as its refrigerant, a super-critical refrigerant usedunder super-critical conditions. The refrigerant circuit of the firstinvention is characterized in that the cooling section 17 capable ofcooling a refrigerant flowing out of the radiator 16 is providedupstream of the receiver 18.

[0013] Since, in the refrigerant circuit of the first invention,refrigerant which flows into the receiver 18 is cooled in the coolingsection 17, this makes it possible to store refrigerant, which has beencooled sufficiently enough to enter the high density state, in thereceiver 18 even when various circumstances et. cetera cause variationsin load on the side of the radiator 16 and on the side of the evaporator20. This allows an adequate amount of refrigerant to circulate throughthe refrigerant circuit.

[0014] A second invention provides a refrigerant circuit which ischaracterized in that a part of the evaporator 20 functions as an airheat exchanger and the air heat exchanger operates as the coolingsection 17.

[0015] In the refrigerant circuit of the second invention, the coolingsection 17 is formed by a part of the evaporator 20, which eliminatesthe need for the provision of an additional heat exchanger, therebymaking it possible to simplify the entire refrigerant circuit.

[0016] A third invention provides a refrigerant circuit which ischaracterized in that the cooling section 17 is operable to transferheat between refrigerant flowing out of the radiator 16 and refrigeranton the outlet side of the evaporator 20.

[0017] In the refrigerant circuit of the third invention, refrigerantpresent on the outlet side of the evaporator 20 is low in temperatureand pressure, thereby ensuring that refrigerant flowing into thereceiver 18 is cooled by such a low temperature, low pressurerefrigerant without fail.

[0018] A fourth invention provides a refrigerant circuit comprising acompressor (15), a radiator 16, a receiver 18, an expansion valve 19,and an evaporator 20. In the refrigerant circuit of the fourthinvention, the compressor 15 compresses refrigerant to above a criticalpressure for performing a refrigerating cycle. The refrigerant circuitof the fourth invention is characterized in that a heat exchange means30 operable to transfer heat between high pressure refrigerant in theinside of the receiver 18 and low pressure refrigerant is provided.

[0019] Stated another way, the fourth invention is a refrigerant circuitwhich is made up of the aforesaid components, i.e., the compressor 15,the radiator 16, the receiver 18, the expansion valve 19, and theevaporator 20. The refrigerant circuit of the fourth invention uses, asits refrigerant, a super-critical refrigerant used under super-criticalconditions. The refrigerant circuit of the fourth invention ischaracterized in that the heat exchange means 30 capable of transferheat between a high pressure refrigerant within the receiver 18 and alow pressure refrigerant is provided.

[0020] In the refrigerant circuit of the fourth invention, it is ensuredthat refrigerant in the inside of the receiver 18 is cooled by lowpressure refrigerant without fail. This makes it possible to promote theaccumulating of refrigerant in the inside of the receiver 18, therebypreventing the receiver 18 from entering the excess refrigerant state.Contrary to the refrigerant in the inside of the receiver 18, the lowpressure refrigerant is heated, thereby making it possible to preventthe compressor 15 from performing a wet operation.

[0021] A fifth invention provides a refrigerant circuit which ischaracterized in that the low pressure refrigerant is refrigerant on theinlet side of the evaporator 20.

[0022] In the refrigerant circuit of the fifth invention, refrigerant onthe inlet side of the evaporator 20 is low in temperature and pressure,thereby ensuring that refrigerant within the receiver 18 is cooled bysuch a low temperature, low pressure refrigerant without fail.

[0023] A sixth invention provides a refrigerant circuit which ischaracterized in that the low pressure refrigerant is refrigerant on theoutlet side of the evaporator 20.

[0024] In the refrigerant circuit of the sixth invention, refrigerant onthe outlet side of the evaporator 20 is low in temperature and pressure,thereby ensuring that refrigerant within the receiver 18 is cooled bysuch a low temperature, low pressure refrigerant without fail.

[0025] A seventh invention provides a refrigerant circuit which ischaracterized in that a main path 54 through which high pressurerefrigerant from the compressor 15, after having passed through theradiator 16, flows into the expansion valve 19, and a bypass circuit 55through which high pressure refrigerant from the compressor 15 flowsinto the receiver 18 are provided, whereby refrigerant, the temperatureof which is higher than the temperature of refrigerant on the outletside of the radiator 16, flows into the receiver 18.

[0026] Stated another way, in the refrigerant circuit of the seventhinvention, the aforesaid paths, i.e., the main path 54 through whichhigh pressure refrigerant from the compressor 15, after having passedthrough the radiator 16, flows into the expansion valve 19 and thebypass circuit 55 through which high pressure refrigerant from thecompressor 15 flows into the receiver 18, are provided, wherebyrefrigerant, the temperature of which is higher than the temperature ofrefrigerant on the outlet side of the radiator 16, flows into thereceiver 18.

[0027] In the refrigerant circuit of the seventh invention, highpressure refrigerant flowing into the receiver 18 is refrigerant thatpasses through the bypass circuit 55, in other words, refrigerant, thetemperature of which is higher than the temperature of refrigerant onthe outlet side of the radiator 16, flows into the receiver 18. Hereby,it becomes possible to increase the temperature variation range ofrefrigerant in the inside of the receiver 18, and the refrigerantdensity difference for every operational area can be increased.

[0028] An eighth invention provides a refrigerant circuit which ischaracterized in that the bypass circuit 55 is provided with a throttlemechanism S.

[0029] In the refrigerant circuit of the eighth invention, the flow rateof refrigerant passing through the inside of the receiver 18 is variedby the throttle mechanism S. This ensures that excess refrigerantgenerated by the difference in operational condition is accumulated inthe receiver 18 without fail, thereby making it possible to achieveimprovements in excess refrigerant absorption capacity.

[0030] A ninth invention provides a refrigerant circuit comprising acompressor 15, a radiator 16, a receiver 18, an expansion valve 19, andan evaporator 20 in which refrigerant circuit the compressor 15compresses refrigerant to above a critical pressure for performing arefrigerating cycle. And a bypass circuit 55 through which high pressurerefrigerant from the compressor 15 flows into the receiver 18 isprovided for transferring heat between high pressure refrigerant in theinside of the receiver 18 and low pressure refrigerant on the inlet sideof the evaporator 20.

[0031] Stated another way, the refrigerant circuit of the ninthinvention is a refrigerant circuit which comprises the aforesaidcomponents, i.e., the compressor 15, the radiator 16, the receiver 18,the expansion valve 19, and the evaporator 20. The refrigerant circuitof the ninth invention uses, as its refrigerant, a super-criticalrefrigerant used under super-critical conditions. The refrigerantcircuit of the ninth invention is characterized in that the bypasscircuit 55 through which high pressure refrigerant from the compressor15 flows into the receiver 18 is provided for transferring heat betweenhigh pressure refrigerant in the inside of the receiver 18 and lowpressure refrigerant on the inlet side of the evaporator 20.

[0032] In the refrigerant circuit of the ninth invention, it is ensuredthat refrigerant within the receiver 18 is cooled by low pressurerefrigerant without fail. This makes it possible to promote theaccumulating of refrigerant in the inside of the receiver 18, therebymaking it possible to prevent the receiver 18 from entering the excessrefrigerant state.

[0033] A tenth invention provides a refrigerant circuit which ischaracterized in that a flow rate control valve 56 is disposed on theoutlet side of the receiver 18.

[0034] In the refrigerant circuit of the tenth invention, it is possibleto rise the refrigerant temperature and reduce the amount of refrigerantstorage in the inside of the receiver 18 when the flow rate controlvalve 56 is fully opened. Additionally, at the time of the valve travelcontrol of the flow rate control valve 56, it is possible to hold therefrigerant temperature at a required level and the amount ofrefrigerant storage in the inside of the receiver 18 is made adequate.When the flow rate control valve 56 is fully closed, it is possible todecrease the refrigerant temperature and increase the amount ofrefrigerant storage in the inside of the receiver 18.

EFFECTS OF INVENTION

[0035] In accordance with the refrigerant circuit of the firstinvention, even when there occur variations in load on the side of theradiator 16 and on the side of the evaporator 20, the amount ofrefrigerant circulating through the refrigerant circuit is maintained atadequate levels, with the result that stable operations are carried outand there is no drop in COP. Besides, the capacity of a receiver to bedisposed can be set low, and the entire refrigerant circuit can bedownsized and the cost of production can be reduced.

[0036] In accordance with the refrigerant circuit of the secondinvention, the need for the provision of an additional heat exchanger iseliminated, thereby making it possible to achieve simplification of theentire refrigerant circuit. Therefore, the cost of production is reducedto a further extent.

[0037] In accordance with the refrigerant circuit of the thirdinvention, it is ensured that refrigerant entering into the receiver 18is cooled without fail. This ensures that the refrigerating cycle ismaintained adequately.

[0038] In accordance with the refrigerant circuit of the fourthinvention, the amount of refrigerant circulating through the refrigerantcircuit is made adequate, even under the condition that conventionalrefrigerant circuits undergo the excess refrigerant state. In otherwords, excess refrigerant generated by the difference in operationalcondition is dealt with in the refrigerant circuit of the fourthinvention, thereby achieving improvements in COP and reducing costs. Onthe contrary, refrigerant on the low pressure side is heated. Thisprevents the compressor 15 from performing a wet compression operation,therefore improving the reliability of the compressor 15.

[0039] In accordance with the refrigerant circuit of the fifth or sixthinvention, it is further ensured that excess refrigerant is dealt with,thereby achieving improvements in COP and reducing costs.

[0040] In accordance with the refrigerant circuit of the seventhinvention, it is possible to increase the refrigerant density differencefor every operational area. This increases the excess refrigerantabsorption capacity, and the drop in refrigeration effect is preventedfrom occurring without fail, and the COP is improved.

[0041] In accordance with the refrigerant circuit of the eighthinvention, it is ensured that the excess refrigerant absorption capacityis improved, and the refrigerant circuit is improved in reliability.

[0042] In accordance with the refrigerant circuit of the ninthinvention, the amount of refrigerant circulating through the refrigerantcircuit is made adequate, even under the condition that conventionalrefrigerant circuits undergo the excess refrigerant state. In otherwords, excess refrigerant generated by the difference in operationalcondition is dealt with in the refrigerant circuit of the ninthinvention, thereby achieving improvements in COP and reducing costs.

[0043] Finally, in accordance with the refrigerant circuit of the tenthinvention, it is ensured that excess refrigerant generated by thedifference in operational condition is dealt with stably.

BRIEF DESCRIPTION OF DRAWINGS

[0044]FIG. 1 is a simplified diagram showing a first embodiment of therefrigerant circuit of the present invention;

[0045]FIG. 2 is a perspective illustration of a cooling section of therefrigerant circuit;

[0046]FIG. 3 graphically represents a refrigerating cycle of therefrigerant circuit;

[0047]FIG. 4 is a simplified diagram showing the refrigerant circuitemploying another cooling section;

[0048]FIG. 5 is a simplified diagram showing the refrigerant circuitemploying still another cooling section;

[0049]FIG. 6 is a front view of the cooling section;

[0050]FIG. 7 is a simplified diagram showing a second embodiment of therefrigerant circuit of the present invention;

[0051]FIG. 8 is a simplified diagram showing a modification example ofthe refrigerant circuit;

[0052]FIG. 9 is a simplified diagram showing a third embodiment of therefrigerant circuit of the present invention;

[0053]FIG. 10 is a simplified diagram showing a modification example ofthe refrigerant circuit;

[0054]FIG. 11 is a simplified diagram showing another modificationexample of the refrigerant circuit;

[0055]FIG. 12 is a simplified diagram showing a fourth embodiment of therefrigerant circuit of the present invention;

[0056]FIG. 13 is a simplified diagram showing a modification example ofthe refrigerant circuit;

[0057]FIG. 14 is a simplified diagram showing another modificationexample of the refrigerant circuit;

[0058]FIG. 15 is a simplified diagram showing a receiver applicable toeach of the refrigerant circuits of FIGS. 7-14;

[0059]FIG. 16 is a simplified diagram showing another receiver;

[0060]FIG. 17 is a simplified diagram showing a fifth embodiment of therefrigerant circuit of the present invention;

[0061]FIG. 18 is a simplified front view showing a receiver applied tothe refrigerant circuit of FIG. 17;

[0062]FIG. 19 is a simplified top plan view showing the receiver appliedto the refrigerant circuit of FIG. 17;

[0063]FIG. 20 is a simplified diagram showing a sixth embodiment of therefrigerant circuit of the present invention;

[0064]FIG. 21 is a cross sectional view of a heating means of therefrigerant circuit;

[0065]FIG. 22 is a simplified diagram showing a state at the time whenthe refrigerant circuit is activated;

[0066]FIG. 23 is a simplified diagram showing a seventh embodiment ofthe refrigerant circuit of the present invention;

[0067]FIG. 24 is a simplified diagram showing an eighth embodiment ofthe refrigerant circuit of the present invention;

[0068]FIG. 25 is a simplified diagram showing a ninth embodiment of therefrigerant circuit of the present invention;

[0069]FIG. 26 graphically represents a refrigerating cycle of aconventional refrigerant circuit;

[0070]FIG. 27 is a simplified diagram of a conventional refrigerantcircuit;

[0071]FIG. 28 graphically represents a refrigerating cycle for thepurpose of describing drawbacks of a conventional refrigerant circuit;and

[0072]FIG. 29 graphically represents a refrigerating cycle for thepurpose of describing drawbacks of a conventional refrigerant circuit.

BEST MODE FOR CARRYING OUT INVENTION

[0073] Hereinafter, concrete embodiments of the refrigerant circuit ofthe present invention will be described in detail with reference to thedrawings. Referring to FIG. 1, there is shown in a simplified manner ahot water supply apparatus of the heat pump type making use of arefrigerant circuit of the present invention. The heat pump type hotwater supply apparatus is made up of a tank unit 1 and a heat sourceunit 2. Water (hot water) held in the tank unit 1 is heated in the heatsource unit 2.

[0074] The tank unit 1 is provided with a hot water storage tank 3, andhot water stored in the hot water storage tank 3 is supplied to a bathtub (not shown) or the like. To this end, the hot water storage tank 3has, at its bottom wall, a water supply port 5. Provided in the upperwall of the hot water storage tank 3 is a hot water discharge port 6.More specifically, a supply of water is delivered to the hot waterstorage tank 3 from the water supply port 5, and high temperature hotwater is delivered from the hot water discharge port 6. In this case, awater supply flow path 8 provided with a check valve 7 is connected tothe water supply port 5, and a water intake port 10 is opened at thebottom wall of the hot water storage tank 3, and a hot water supply port11 is opened at an upper portion of the side wall (circumferential wall)of the hot water storage tank 3. And, the water intake port 10 and thewater supply port 11 are linked together by a circulation path 12, and awater circulation pump 13 and a heat exchange path 14 are inserted inthe circulation path 12.

[0075] The hot water storage tank 3 is provided with four detectors 47a, 47 b, 47 c, 47 d for detecting the remaining amount of hot water(hereinafter called the “hot water remaining amount detectors”) whichare vertically disposed at given pitches. Further, a temperature sensor48 is mounted on the upper wall of the hot water storage tank 3. The hotwater remaining amount detectors 47 a, 47 b, 47 c, 47 d and thetemperature sensor 48 are implemented by thermistors. Additionally, inthe circulation path 12, a water intake thermistor 64 is disposed on theupstream side of the heat exchange path 14 (more specifically, on theupstream side of the pump 13), and a hot water discharge thermistor 65is disposed on the downstream side of the heat exchange path 14.

[0076] Furthermore, the heat source unit 2 is provided with arefrigerant circuit R formed in accordance with the present invention.The refrigerant circuit R is formed by sequential connection of acompressor 15, a water heat exchanger (condenser) 16 which constitutesthe heat exchange path 14, a cooling section 17, a receiver 18, anexpansion valve 19 which constitutes a pressure reducing mechanism, andan evaporator 20. And, as the refrigerant of the refrigerant circuit R,for example, carbon dioxide (CO₂) which is compressed to above acritical pressure is used. The refrigerant of the refrigerant circuit Ris carbon dioxide used in so-called super-critical conditions. It shouldbe noted that the condenser 16 is a device having a function of coolinga high temperature, high pressure super-critical refrigerant compressedin the compressor 15. The condenser 16 is called, in some cases, a gascooling apparatus or a radiator.

[0077] The cooling section 17 cools refrigerant flowing out of thecondenser 16, and is formed by a liquid gas heat exchanger 21 shown inFIG. 2. The liquid gas heat exchanger 21 has a double pipe structure,and is made up of a first passage way 22 through which refrigerant fromthe condenser 16 passes and a second passage way 23 through whichrefrigerant from the evaporator 20 passes. In other words, the firstpassage way 22 forms a part of a refrigerant flow path 24 by which thecondenser 16 and the receiver 18 are connected together, while thesecond passage way 23 forms a part of a refrigerant flow path 25 bywhich the evaporator 20 and the compressor 15 are connected together.Accordingly, the cooling section 17 serves as a refrigerant-refrigerantheat exchanger, and heat is transferred between a high pressure, hightemperature refrigerant passing through the first passage way 22 and alow pressure, low temperature refrigerant passing through the secondpassage way 23, whereby refrigerant flowing into the receiver 18 iscooled. Additionally, the low pressure refrigerant is heated, therebymaking it possible to prevent the compressor 15 to performing a wetcompression operation.

[0078] In the refrigerant circuit R, a refrigerant flow path 40 by whichthe compressor 15 and the water heat exchanger 16 are connected togetherand a refrigerant flow path 41 by which the expansion valve 19 and theevaporator 20 are connected together are linked together by a bypasscircuit 42, and a defrost valve 43 is disposed in the bypass circuit 42.The refrigerant flow path 40 is provided with an HPS 45 as a pressureprotection switch and a pressure sensor 46. The bypass circuit 42 is tosupply a hot gas discharged from the compressor 15 to the evaporator 20,whereby defrost operations to defrost the evaporator 20 are performed.To this end, the heat source unit 2 is provided with a defrost controlmeans (not shown) for establishing switching between the normal waterheating operation and the defrost operation. Stated another way, duringthe normal water heating operation, the water heat exchanger 16functions as a condenser for heating hot water passing through the heatexchange path 14. On the other hand, during the defrost operation, theexpansion valve 19 is placed in the fully closed state while the defrostvalve 43 is placed in the open state for allowing hot gas to flow intothe evaporator 20. The evaporator 20 is heated by the hot gas, therebypreventing the generation of frost in the evaporator 20. The defrostcontrol means is implemented, for example by the use of a microcomputer.

[0079] Next, the operational action (water heating operation) of therefrigerant circuit R will be described.

[0080] When the compressor 15 is activated while the water circulationpump 13 is activated or brought in operation, stored water (hot water)starts flowing out of the water intake port 10 provided at the bottom ofthe hot water storage tank 3 and flows in the heat exchange path 14 ofthe circulation path 12. At this time, the hot water is heated (boiled)by the water heat exchanger which is the condenser 16. Thereafter, thehot water is returned to the upper part of the hot water storage tank 3from the water supply port 11. This operation is carried outcontinuously, whereby hot water is stored in the hot water storage tank3. In the current electricity rate, the nighttime electricity unit costis lower than the daytime electricity unit cost. Therefore, preferablythe operation is carried out in late night hours during which theelectricity unit cost is low, for the purpose of reducing costs.

[0081] When warm water is being boiled, high temperature hot water flowsout into the circulation path 12 from the water intake port 10 if hightemperature warm water is stored to the bottom of the hot water storagetank, with the result that the temperature of water entering into thewater heat exchanger 75 rises. In a conventional refrigerant circuit, ifthe temperature of water entering into the water heat exchanger 16rises, the refrigerating cycle shown in FIG. 26 becomes a refrigeratingcycle as indicated by solid line of FIG. 28. Because of this,circulating refrigerant enters the excessive state (excess refrigerantstate).

[0082] However, since the refrigerant circuit R shown in FIG. 1 isprovided with the cooling section 17, refrigerant is cooledsufficiently, and, on the high pressure side in front of the expansionvalve 19, high density refrigerant is accumulated in the inside of thereceiver 18. In other words, excess refrigerant processing is carriedout, thereby making the amount of refrigerant circulating in therefrigerant circuit R adequate, and the refrigerant cycle as shown inFIG. 3 results. This makes it possible to perform stable operations, andthe drop in COP does not take place. Besides, the capacity of a receiverto be disposed can be set low, and the entire refrigerant circuit can bedownsized and the cost of production can be reduced. It is possible tocarry out stable operations.

[0083] Referring next to FIG. 4, there is shown a refrigerant circuit Rin which the cooling section 17 is formed by an air heat exchanger 26.The cooling section 17 has a flow path constituting a part of therefrigerant flow path 24 by which the condenser 16 and the receiver 18are connected together, and, when refrigerant passes through the flowpath, it exchanges heat with air. Because of this, the amount ofrefrigerant which is accumulated in the inside of the receiver 18 iscontrolled also by the cooling section 17, thereby making the amount ofrefrigerant which circulates through the refrigerant circuit R adequate.It becomes possible to carry out stable operations.

[0084] Referring to FIG. 5, there is shown a refrigerant circuit R inwhich a part of the evaporator 20 functions as an air heat exchangerserving as the cooling section 17. Stated another way, in this case theevaporator 20 is made up of a main body 27 having a great number of finsand first and second tubes 28 and 29 disposed in the inside of the mainbody 27. And, refrigerant from the expansion valve 19 passes through thefirst tube 28, and refrigerant from the condenser 16 passes through thesecond tube 29. That is, the original evaporation function is achievedby the main body 27, the first tube 28 et cetera, while the main body27, the second tube 29 et cetera together function as the coolingsection (air heat exchanger) 17 for cooling refrigerant flowing out ofthe condenser 16.

[0085] In this case, the first tube 28 is formed into a snaking shape,and has openings 28 a and 28 b both of which are opened on the side of aside surface 27 a of the main body 27. Additionally, the second tube 29is formed into a U-shape, and has openings 29 a and 29 b both of whichare opened on the side of the side surface 27 a of the main body 27.Such an arrangement that a part of the evaporator 20 constitutes thecooling section 17 is not limited to the one as shown in FIG. 6. Forexample, the dimensions of the main body 27 and the length dimension ofthe first and second tubes 28 and 29 may be changed in a free manner.

[0086] Accordingly, the refrigerant circuit R of FIG. 5 is able to dealwith excess refrigerant caused by the environmental variation such asthe rise in water entrance temperature (the temperature of waterentering into the water heat exchanger 16), as in the refrigerantcircuit of FIG. 1. This makes the amount of refrigerant which circulatesthrough the refrigerant circuit R adequate, thereby making it possibleto ensure stable operations. Besides, neither the heat exchanger 21 asshown in FIG. 1 nor the heat exchanger 26 as shown in FIG. 4 isrequired, and the cooling section 17 is formed by a part of theevaporator 20 naturally necessary for such a type of refrigerantcircuit, thereby making it possible to both downsize the entirerefrigerant circuit R and reduce the cost of production.

[0087] Referring next to FIG. 7, there is shown a refrigerant circuit Rin which the receiver 18 shown in FIG. 15 is used for transferring heatbetween a high pressure refrigerant in the inside of the receiver 18 anda low pressure refrigerant. In other words, an inflow pipe 50 into whichrefrigerant from the condenser 16 flows, and an outflow pipe 51 by wayof which refrigerant from the receiver 16 flows into the expansion valve19 are connected to the receiver 18, and the refrigerant flow path 41connecting together the expansion valve 19 and the evaporator 20 ispenetrated through the receiver 18. Hereby, a heat exchange means 30capable of transferring heat between a high pressure refrigerant flowinginto the receiver 18 from the inflow pipe 50 and a low pressurerefrigerant flowing in the refrigerant flow path 41, is constituted.

[0088] In accordance with the refrigerant circuit R of FIG. 7, it isensured that heat is transferred without fail because refrigerant on thelow pressure side for transferring heat is refrigerant on the inlet sideof the evaporator 20, thereby making it possible to promote theaccumulating of refrigerant in the inside of the receiver 18. Because ofthis, even under the condition that excess refrigerant is generated, theamount of refrigerant circulating through the refrigerant circuit R isheld adequate, thereby preventing the occurrence of a wet operation andthe drop in COP.

[0089] Referring to FIG. 8, there is shown a refrigerant circuit R inwhich the refrigerant flow path (suction flow path) 25, by which theevaporator 20 and the compressor 15 are connected together, ispenetrated through the receiver 18. Hereby, the heat exchange means 30capable of transferring heat between a high pressure refrigerant in theinside of the receiver 18 and a low pressure refrigerant flowing in therefrigerant flow path 25, is constituted, thereby making it possible toboth promote the accumulating of refrigerant in the inside of thereceiver 18 and avoid the excess refrigerant state.

[0090] Referring next to FIG. 9, there is shown a refrigerant circuit Rwhich comprises a main passage way 54 through which refrigerant from thecompressor 15, after having passed through the condenser 16 and the heatexchanger 49, flows into the expansion valve 19, and a bypass circuit 55by which a flow of refrigerant branches off from the main passage way 54and merges with the main passage way 54 via the receiver 18. In otherwords, the main passage way 54 has a refrigerant flow path 40 (which isa refrigerant discharge path of the compressor 15) and a connecting pipe57 extending from the condenser 16 and connected to the expansion valve19 via the heat exchanger 49 (which is a heat exchanger for thesupercooling of refrigerant flowing out of the condenser 16), while thebypass circuit 55 has a first pipe 58 which branches off from therefrigerant discharge path 40 and is connected to the receiver 18 and asecond pipe 59 extending from the receiver 18 and connected to the mainpassage way 54. The heat exchanger 49 is operable to transfer heatbetween a refrigerant flowing in the connecting pipe 57 and arefrigerant flowing in the refrigerant flow path 25.

[0091] In accordance with the refrigerant circuit R of FIG. 9, in themain passage way 54, high pressure refrigerant from the compressor 15flows in the following course: CONDENSER 16→HEAT EXCHANGER 49→EXPANSIONVALVE 19→EVAPORATOR 20→RECEIVER 18→HEAT EXCHANGER 49→COMPRESSOR 15.Because of this, in the condenser 16 serving as a water heat exchanger,hot water circulating through the circulation path 12 (not shown) isheated. Additionally, in the bypass circuit 55, high pressurerefrigerant from the compressor 15 flows into the receiver 18 and flowsinto the expansion valve 19 from the receiver 18. The refrigerant flowsout of the evaporator 20, and is brought back to the compressor 15 byway of the refrigerant flow path 25. This constitutes the heatexchanging means 30 capable of transferring heat between a high pressurerefrigerant which has flowed into the receiver 18 from the first pipe 58and a low pressure refrigerant which is flowing in the refrigerant flowpath 25.

[0092]FIG. 10 shows a refrigerant circuit R in which the condenser 16and the receiver 18 are connected together by the first pipe 58, andFIG. 11 shows a refrigerant circuit R in which the outlet of thecondenser 16 and the receiver 18 are connected together by the firstpipe 58. Also in these refrigerant circuits R, heat is transferredbetween a high pressure refrigerant in the inside of the receiver 18 anda low pressure refrigerant flowing in the refrigerant flow path 25.

[0093]FIG. 12 shows a refrigerant circuit R which is similar to therefrigerant circuit R of FIG. 10, with the exception that a throttlingmechanism S (e.g., a capillary tube) is inserted in the first pipe 58.FIG. 13 shows a refrigerant circuit R which is similar to therefrigerant circuit R of FIG. 10, with the exception that a throttlingmechanism S (e.g., a capillary tube) is inserted in the second pipe 59.In these cases, the flow rate of refrigerant passing through thereceiver 18 can be varied. In other words, it is ensured that excessrefrigerant generated by the difference in operational condition isaccumulated in the inside of the receiver 18, thereby making it possibleto achieve improvements in excess refrigerant absorption capacity.Furthermore, FIG. 14 shows a refrigerant circuit R which employs anelectric valve in place of the throttling mechanism S and exhibits thesame effects that the refrigerant circuit R shown in FIG. 13 does.Accordingly, the refrigerant circuit R shown in FIG. 12 may employ anelectric valve in place of a capillary tube. Furthermore, in therefrigerant circuits R shown in FIGS. 9 and 11, the bypass circuit 55may be provided with the throttling mechanism S.

[0094] In the refrigerant circuits R of FIGS. 7 and 8, the refrigerantstate in the inside of the receiver 18 is determined by the outlet stateof the water heat exchanger (condenser) 16. Therefore, the excessrefrigerant absorption capacity of the receiver is: (the refrigerantdensity at the water heat exchanger's 16 outlet)×volume. Accordingly, inthese refrigerant circuits, the absorption capacity is not very great.On the other hand, in the refrigerant circuits R of FIGS. 9, 10, 12 and13, it is possible to accumulate a refrigerant the temperature of whichis different from the outlet temperature of the water heat exchanger(condenser) 16, i.e., a refrigerant whose temperature is higher than theoutlet temperature. Hereby, the refrigerant density difference for everyoperational area can be increased, therefore enhancing the excessrefrigerant absorption capacity. In this case, the refrigerant circuit Rshown in FIG. 9 exhibits the greatest excess refrigerant absorptioncapacity, the reason for which is that its refrigerant temperaturevariation range in the inside of the receiver 18 is greatest.Furthermore, comparison in heat loss (the amount of liberation of heatto other than water in the water heat exchanger) was made with respectto the refrigerant circuits R of FIGS. 9-11. The refrigerant circuit Rshown in FIG. 9 is greatest in heat loss. The refrigerant circuit Rshown in FIG. 10 is less in heat loss than the refrigerant circuit Rshown in FIG. 9. The refrigerant circuit R shown in FIG. 11 is least inheat loss, the reason for which is that the first pipe 58 branches offfrom the outlet side of the condenser 16 in the refrigerant circuit R ofFIG. 11.

[0095] It may be arranged such that the receiver 18 of each of therefrigerant circuits R shown in FIGS. 7-14 is implemented by the oneshown in FIG. 16. When employing such arrangement, either therefrigerant flow path 41 or the refrigerant flow path 25 is made toextend along an external surface of the receiver 18, whereby heat istransferred between a high pressure refrigerant in the inside of thereceiver 18 and a low pressure refrigerant flowing in the refrigerantflow path 41 (or the refrigerant flow path 25). In the case where therefrigerant flow path 41 (or the refrigerant flow path 25) is made toextend along the receiver 18, it may be either disposed linearlyparallelly or wound around the outer peripheral surface of the receiver18.

[0096] In each of the refrigerant circuits R shown in FIGS. 9-14, it maybe arranged such that the first pipe 58 of the bypass circuit 55 isconnected to an upstream portion of the water heat exchanger 16 whilethe second pipe 59 of the bypass circuit 55 is connected to anintermediate portion of the water heat exchanger 16, as indicated byvirtual line. As a result of such connecting arrangement, it becomespossible to reduce heat loss and optimize the rise in inlet refrigeranttemperature of the receiver 18. In this case, the main passage way 54 isa passage way as indicated by solid line (see FIGS. 9-14). As in therefrigerant circuits R of FIGS. 9-14 provided with the receiver 18 andthe heat exchanger (liquid gas heat exchanger) 49, the order in whichthey are disposed may be in reverse with respect to the examples shownin the figures.

[0097] As shown in FIG. 17, it may be arranged such that the bypasscircuit 55, which branches off from the condenser 16 and merges with thecondenser 16 at a location downstream of the branch point and thereceiver 18, is inserted in the bypass circuit 55 for transferring heatbetween a high pressure refrigerant in the inside of the receiver 18 anda low pressure refrigerant on the inlet side of the evaporator 20.Stated another way, the main passage way 54, by way of which highpressure refrigerant from the compressor 15, after having passed throughthe condenser 16, flows into the expansion valve 19, has the refrigerantdischarge path 40 and the connecting pipe 57, and the bypass circuit 55is connected to the main passage way 54.

[0098] More specifically, in the bypass circuit 55, the first pipe 58 isconnected to a point slightly upstream of the intermediate part of thecondenser 16 while the second pipe 59 is connected to a point slightlydownstream of the intermediate part of the condenser 16. Interposedbetween the first pipe 58 and the second pipe 59 is the receiver 18. Asa result of such arrangement, a flow of high pressure refrigerantbranched off from the main passage way 54 passes through the receiver 18and merges with the main passage way 54, in other words the highpressure refrigerant flows back to the main passage way 54.

[0099] Also in this case, refrigerant in the main passage way 54 flowsin the connecting pipe 57 and, therefore, flows into the expansion valve19 via the heat exchanger 49 which is a heat exchanger for thesupercooling of refrigerant flowing out of the condenser 16.

[0100] And, as shown in FIGS. 18 and 19, the receiver 18 is heatexchangeably disposed in a side-by-side relationship with therefrigerant flow path 41 which is a low pressure pipe by which theexpansion valve 19 and the evaporator 20 are connected together. Inother words, a section of the refrigerant flow path 41 that extendsalong the receiver 18 is zigzag-shaped, and projecting portions 41 a, .. . in proximity to or in contact with the receiver 18 are connected toan outer wall 18 a of the receiver 18 by connecting means such asbrazing. Hereby, heat is transferred between a high pressure refrigerantpassing through the receiver 18 and a low pressure refrigerant flowingin the refrigerant flow path 41. At this time, the connection areaswhere the refrigerant flow path 41 and the receiver 18 are brought intocontact with each other are scattered, thereby preventing local heatexchange, in other words total heat exchange is carried out. Of course,it may be arranged such that the refrigerant flow path 41, which is notzigzag-shaped, extends along the outer wall 18 a of the receiver 18 anda section of the refrigerant flow path 41 in proximity to or in contactwith the receiver 18 is connected thereto by connecting means such asbrazing.

[0101] Furthermore, as shown in FIG. 17, a flow rate control valve 56implemented by an electric valve is inserted in the second pipe 59 bywhich the receiver 18 and the condenser 16 are connected together. Inother words, the flow rate control valve 56 is provided on the outletside of the receiver 18. When the flow rate control valve 56 is fullyopened, the refrigerant temperature rises and the amount of refrigerantstorage in the inside of the receiver 18 decreases. At the time ofcontrolling the valve travel of the flow rate control valve 56, therefrigerant temperature is held at a level required and the amount ofrefrigerant storage in the inside of the receiver 18 is made adequate.When the flow rate control valve 56 is fully closed, the refrigeranttemperature falls and the amount of refrigerant storage in the inside ofthe receiver 18 increases. This ensures that excess refrigerantgenerated by the difference in operational condition is dealt withstably without fail.

[0102] In the refrigerant circuit of FIG. 17, a defrost valve 43 isinserted in the defrost pipe line (bypass circuit) 42. In other words,the defrost pipe line 42 branching off from the refrigerant dischargepath 40 is connected to the refrigerant flow path 41 on the inlet sideof the evaporator 20. This prevents heat loss during the defrostoperation.

[0103] As described above, also in the refrigerant circuit of FIG. 17,the accumulating of refrigerant in the inside of the receiver 18 ispromoted, thereby avoiding the excess refrigerant state. In addition,also in the refrigerant circuit of FIG. 17, the change in position ofthe branch part and the merging part of the bypass circuit 55 can bemade in a free manner as shown by solid and virtual lines of FIGS. 9-14.For example, it may be arranged such that the first pipe 58 of thebypass circuit 55 is connected to an upstream part of the condenser 16while the second pipe 59 of the bypass circuit 55 is connected to adownstream part of the condenser 16. To sum up, it suffices if there isgenerated a difference in pressure level between the first pipe 58 andthe second pipe 59 in front of the expansion valve 19.

[0104] The refrigerant circuit R includes, in some cases, an accumulatorfor preventing the occurrence of liquid back to the compressor 15.However, there are problems with the provision of such an accumulator.That is, the cost of production increases and the suction pressure lossof the compressor 15 increases, resulting in reductions in the COP, andthere occurs abnormal noise in the accumulator.

[0105] To cope with the above problems, it is preferable that a heatingmeans 33 for liquid back prevention is disposed in a refrigerant suctionpath 32 (which is a flow path of the refrigerant flow path 25 extendingfrom the cooling section 17 to the compressor 15) of the compressor 15,as shown in FIG. 20. In this case, the heating means 33 is implementedby an electromagnetic induction heater, and comprises a bobbin 34 and anelectromagnetic induction heating heater (coil) 35 which is wound aroundthe bobbin 34, as shown in FIG. 21. Stated another way, the bobbin 34 ismade up of a tubular part 34 a and outer collar parts 34 b and 34 bformed continuously to both ends of the tubular part 34 a, and theelectromagnetic induction heating heater 35 is wound around the tubularpart 34 a.

[0106] And, an iron pipe 36 and an insulating material 37 with which tocover the iron pipe 36 are internally fitted in the tubular part 34 aand an insulating material 38 is externally fitted around theelectromagnetic induction heating heater 35. And, the iron pipe 36constitutes a part of the refrigerant suction path 32. Additionally, theheating means 33 has a power supply (not shown) for supplying electricpower to the electromagnetic induction heating heater 35. When electricpower is supplied from the power supply to the electromagnetic inductionheating heater 35, numerous eddy currents are generated in the iron pipe36, whereby the iron pipe 36 is heated. As a result, refrigerant flowingin the iron pipe 36 is heated.

[0107] Furthermore, the control section of the refrigerant circuit R hasa control means (not shown) for controlling the heating means 33. Inother words, as shown in FIG. 20, thermistors 60 and 61 are disposed inthe vicinity of a suction port of the refrigerant suction path 32 and inthe vicinity of a discharge port of the refrigerant discharge path 40,respectively. The evaporator 20 is provided with an evaporatorthermistor 62. Based on the action of the evaporator thermistor 62 andon the action of the thermistor 60 of the refrigerant suction path 32,it is determined whether liquid back to the compressor 15 will occur ornot. And, if there is the possibility of the occurrence of liquid back,electric power is supplied to the heating means 33 so that refrigerantin the refrigerant suction path 32 is heated. In FIG. 20, referencenumeral 63 denotes an outside air thermistor. Although theirdiagrammatic representation is omitted, the thermistors 60, 61, 62, 63are provided also in each of the refrigerant circuits R, for example inthe refrigerant circuit R of FIG. 1.

[0108] To sum up, in the refrigerant circuit shown in FIG. 20, in thetransition period such as defrost operation and defrost return, theheating means 33 is operated by the control means so that refrigerant inthe refrigerant suction path 32 is heated, thereby preventing theoccurrence of liquid back to the compressor 15. The provision of theheating means 33 makes it possible to prevent the occurrence of liquidback without having to provide an accumulator, thereby both reducingcosts and preventing the drop in COP due to the suction pressure loss.Besides, the cause of generation of abnormal noise is eliminated,thereby achieving quiet operations.

[0109] Furthermore, in this case, the heating means 33 is implemented byan electromagnetic induction heater, which provides advantages such ascleanliness, safety and high heat efficiency. And now, if, in therefrigerant circuit R, either the expansion valve 19 which is anelectric valve is fully closed or the valve travel of the expansionvalve 19 is less than a predetermined value for a given length of timefrom the activation of the compressor 15, this makes it possible toprevent the occurrence of abrupt liquid back of the refrigerant presentin a heavy-line part (high pressure part) of FIG. 22 toward thecompressor 15.

[0110] In addition, in a refrigerant circuit R of FIG. 23, a controlvalve 66 which is an electric valve for flow rate control is insertedupstream of the heating means 33 in the refrigerant suction path 32. Inother words, in the refrigerant circuit R of FIG. 23, by reducing thevalve travel of the control valve 66 in the transition period such asoperation activating time, defrost operation starting time, defrostoperation time, and defrost return time, the flow rate is restricted,and, at the same time, heating is carried out by the heating means 33,for preventing the occurrence of liquid back. This more reliablyachieves liquid back prevention.

[0111] Referring next to FIG. 24, there is shown a refrigerant circuit Rin which a liquid back preventing valve 67 which is an electromagneticvalve is disposed interposingly between the compressor 15 and thecondenser 16. In this case, for a given length of time from theactivation of the compressor 15 or during the defrost operation, eitherthe expansion valve 19 which is an electric valve is fully closed or thevalve travel of the expansion valve 19 is set less than a predeterminedvalue while at the same time the liquid back preventing valve 67 whichis an electromagnetic valve is placed in the closed state. Thistherefore makes it possible to prevent the occurrence of abrupt liquidback of the refrigerant present in a heavy-line part (high pressurepart) (the range from the liquid back preventing valve 67 to theexpansion valve 19) to the compressor 15. In addition, also in therefrigerant circuit R of FIG. 24, the heating means 33 is disposed inthe refrigerant suction path 32, thereby making it possible to preventthe occurrence of liquid back by heating the refrigerant in therefrigerant suction path 32 with the heating means 33 at the operationactivating time or at the defrost operation starting time. Furthermore,also in the refrigerant circuit R shown in FIG. 24, it may be arrangedsuch that the control valve 66 is disposed in the refrigerant suctionpath 32 and the flow rate is restricted by the control valve 66 inaddition to heating by the heating means 33.

[0112] Referring next to FIG. 25, there is shown a refrigerant circuit Rin which the heating means 33 is not provided and the refrigerantsuction path 32 and refrigerant discharge path 40 of the compressor 15are provided with for example liquid back preventing valves 68 and 69,respectively, whereby the occurrence of liquid back to the compressor 15after the operation is brought into a halt is avoided. Stated anotherway, after the operation is stopped, both the liquid back preventingvalves 68 and 69 are placed in the closed state so that refrigerant isprevented from flowing into the compressor 15 through the refrigerantsuction path 32 and through the refrigerant discharge path 40, wherebyactivation defects at the time of the next activation of the compressor15 and damage to the compressor 15 due to liquid compression areavoided. In addition, also in the refrigerant circuit R of FIG. 25, itmay be arranged such that the heating means 33 is disposed in therefrigerant suction path 32 for preventing the occurrence of liquid backto the compressor 15 by heating refrigerant with the heating means 33 inthe transition period such as operation activating time, defrostoperation starting time, defrost operation time, and defrost returntime.

[0113] And, the heating means 33, used in the refrigerant circuits suchas the one shown in FIG. 20, may be formed by other than anelectromagnetic induction heater, in other words the heating means 33may be formed by an heating element of Nichrome (trademark) element orthe like. In addition to the aforesaid liquid back preventing operation,it is preferable that refrigerant in the inside of the compressor 15 isevaporated by performing an open-phase preheating operation of aninverter circuit of the compressor 15 until a predetermined length oftime elapses from the time when the compressor 15 is turned on.

[0114] In the above, various embodiments of the present invention havebeen described. However, the present invention is not limited to theseembodiments and, therefore, various changes and modifications may bemade in the present invention. For example, the present invention isapplicable to refrigerant circuits other than the heat pump type hotwater supply apparatus. In addition, as the refrigerant, refrigerantsused in the super-critical conditions such as ethylene, ethane, nitrogenoxide et cetera may be used in addition to carbon dioxide. The condenser16 of the present invention is any device having a function of cooling ahigh temperature, high pressure super-critical refrigerant compressed bythe compressor 15 and is called, in some cases, a gas cooler (radiator).

INDUSTRIAL APPLICABILITY

[0115] As has been described above, the present invention providesrefrigerant circuits useful for hot water supply apparatus. Therefrigerant circuits of the present invention are particularly suitablefor the case where refrigerant is compressed to above a criticalpressure for performing a refrigerant cycle.

What is claimed is:
 1. A refrigerant circuit comprising a compressor(15), a radiator (16), a receiver (18), an expansion valve (19), and anevaporator (20) in which refrigerant circuit said compressor (15)compresses refrigerant to above a critical pressure for performing arefrigerating cycle, wherein a cooling section (17), for cooling arefrigerant flowing out of said radiator (16), is disposed on theupstream side of said receiver (18).
 2. The refrigerant circuit of claim1, wherein a part of said evaporator (20) constitutes an air heatexchanger and said air heat exchanger operates as said cooling section(17).
 3. The refrigerant circuit of claim 1, wherein said coolingsection (17) is operable to transfer heat between refrigerant flowingout of said radiator (16) and refrigerant on the outlet side of saidevaporator (20).
 4. A refrigerant circuit comprising a compressor (15),a radiator (16), a receiver (18), an expansion valve (19), and anevaporator (20) in which refrigerant circuit said compressor (15)compresses refrigerant to above a critical pressure for performing arefrigerating cycle, wherein heat exchange means (30) operable totransfer heat between high pressure refrigerant in the inside of saidreceiver (18) and low pressure refrigerant is provided.
 5. Therefrigerant circuit of claim 4, wherein said low pressure refrigerant isrefrigerant on the inlet side of said evaporator (20).
 6. Therefrigerant circuit of claim 4, wherein said low pressure refrigerant isrefrigerant on the outlet side of said evaporator (20).
 7. Therefrigerant circuit of claim 4, wherein a main path (54) through whichhigh pressure refrigerant from said compressor (15), after having passedthrough said radiator (16), flows into said expansion valve (19), and abypass circuit (55) through which high pressure refrigerant from saidcompressor (15) flows into said receiver (18) are provided, wherebyrefrigerant, the temperature of which is higher than the temperature ofrefrigerant on the outlet side of said radiator (16), flows into saidreceiver (18).
 8. The refrigerant circuit of claim 7, wherein saidbypass circuit (55) is provided with a throttle mechanism (S).
 9. Arefrigerant circuit comprising a compressor (15), a radiator (16), areceiver (18), an expansion valve (19), and an evaporator (20) in whichrefrigerant circuit said compressor (15) compresses refrigerant to abovea critical pressure for performing a refrigerating cycle, wherein abypass circuit (55) through which high pressure refrigerant from saidcompressor (15) flows into said receiver (18) is provided fortransferring heat between said high pressure refrigerant in the insideof said receiver (18) and low pressure refrigerant on the inlet side ofsaid evaporator (20).
 10. The refrigerant circuit of claim 9, wherein aflow rate control valve (56) is disposed on the outlet side of saidreceiver (18).